paving, also called pervious paving or "porous pavement",
is a term used to describe paving methods for roads, parking lots and
walkways that allow the movement of water and air through the paving
material. Although some porous paving materials appear nearly indistinguishable
from nonporous materials, their environmental effects are qualitatively
different. Their effects are important because pavements are two-thirds
of the potentially impervious surface cover in urban areas.
of permeable paving
Permeable paving surfaces are
highly desirable because of the problems associated with water runoff
from paved surfaces. Part of the problem is creating an unnatural volume
of runoff from precipitation, which causes serious erosion and saltation
in streams and other bodies of waters and also the washing off of vehicular
Permeable paving surfaces keep the pollutants in place in the soil or
other material underlying the roadway, and allow water seepage to recharge
groundwater while preventing the stream erosion problems.
They capture the heavy metals that fall on them, preventing them from
washing downstream and accumulating inadvertently in the environment.
In the void spaces, naturally occurring micro-organisms digest car oils,
leaving little but carbon dioxide and water; the oil ceases to exist
as a pollutant.
Rainwater infiltration through the pavement into the underlying soil
reduces stormwater volume and restores natural subsurface flow paths.
The cost of porous pavement, with its built-in stormwater management,
is usually less that that of an impervious pavement with a separate
stormwater management facility somewhere downstream. Porous pavements
give urban trees the rooting space they need to grow to full size.
A “structural-soil” pavement base combines structural aggregate
with soil; a porous surface admits vital air and water to the rooting
This integrates healthy ecology and thriving cities, with the living
tree canopy above, the city’s traffic on the ground, and living
tree roots below.